28 THE HUMAN STERNUM 



it, and one explains its occurrence on the sume prrounds as that of other 

 centres — mechanical causes. It is useless to i^uote the text-hook statements 

 on this point. Thev are copied from one to another, without verification, 

 and all are more or less erroneous. The statement that is most approximate 

 to the truth, as 1 have ohserved it, is l)wK;n'r's'^: 'hew examples occur 

 over twenty years m which tlie niesosternum is not one pece.' 



3. Croivi/i of the Metasternum 



The date ot ossification of the metasternum is extremely varialile. A 

 centre is usually absent before five years, anil [iresent attei- ei_;hteen \cars, 

 and may ajipear at any date between five and eighteen (Table IX). It 

 appears never to bect^me completel\- r)ss '(m^A^ being touiul tipped with 

 cartilage even in extreme old a;_;e. 



It IS alwaj's ossified by a median centre, which is practically always 

 single. Only three cases occur in \x\\ ccjllection of additional < issificat ons. 

 Two arc examples of additional endoeiiondral ossifications at the extremity 

 of the main centre. The third case is peculiar : in this two small bilateral 

 nodules are interpolated between the inesoslernum and the metasternum. 



(f) Union of the MivsosrERNUM wrrn riii; Presi'ernum and 

 Metasternum (Takle X) 



I. Union of ihe Mesosierniini \viili I lie Presternum. 



Fusion ot the mesosternum with the presternum must be regarded 

 as an abnormalit)'. It occurs in S'lj per cent, ot the six hundred and 

 forty-two sterna examined. Its frcqueiic\' increases with age. fusion 

 occurs in 3'i per cent, of sterna under thirt\', in iO"5 jier cent, between 

 thirty and forty-nine, and in i 5-6 per cent, between fifty and eight\-two. 

 At the same time it is not altogether a se;iile condition. Among tort\-six 

 sterna between sixt\'-one and eighty-two \ears, union of the piesternum aiid 

 mesosternum only occurs four times (8*7 per cent.) ; and among twenty- 

 two sterna between sixty-six antl eii>ht\'-two it only occurs once. 



On the other hand there are grounds tor believin"; that in some cases 

 this condition is associated with the occurrence of an arthrodial joint 

 between the presternum and first costal cartilage (PI. VI, Idg. 40). A close 



